The present invention provides a device for increasing the dynamic range of frequency-modulated continuous-wave radar.
A distinction is made in the broad sense between pulsed and continuous-wave designs of radar systems.
Pulsed radar determines the distance of a target object from a radar receiver from the transit time of pulses (echo signals) reflected by a target object. To compensate for the great differences in the echo signals to be processed in the radar receiver from short and great distances (near echos and far echos), the distance dynamics as it is called, the sensitivity of the radar receiver is regulated in pulsed radar as a function of time (sensitivity time control, or STC) so that at the beginning of the reception period, a low sensitivity is combined with a high echo level from the near range and vice versa.
In contrast with pulsed radar, continuous-wave radar operates with a continuously emitted transmission signal. With pulsed radar, the transmission signal can be separated from the echo signal by the fact that both signals occur at different times, but with continuous-wave radar, the transmission signals are separated and differentiated from the echo signals by modulation of the wave, i.e., by frequency modulation in practice.
The concept of time-dependent sensitivity of the radar receiver, which is known from pulsed radar, cannot be used with continuous-wave radar, in particular frequency-modulated continuous-wave radar (FM CW radar), because all the echo signals of the target object always have to be processed at the same time, so no differentiation in time is possible.
It is known here that the dynamics of the video signals or intermediate frequency signals generated in the radar receiver from the echo signals can be reduced before further processingxe2x80x94e.g., by an analog/digital converter modulexe2x80x94by using a high-pass filter of suitable dimensions. Thus, the low video frequencies belonging to near targets (near echos) are reduced to a greater extent than higher video frequencies belonging to more remote targets (far echos).
However, this measure acts only downstream from the high frequency component of the radar receiver, so that when multiple signals coincide, especially signals of extremely different levels (such as near and far echos), additional signals are generated due to intermodulation and other nonlinear processes and are interpreted as target objects (unwanted false targets) by the radar.
The range and other system parameters of frequency-modulated continuous-wave radar are therefore determined to a great extent by the full-power signal strength of the high-frequency components of the radar receiver, the dynamic range between the largest processable signal level and the lower sensitivity limit (noise level). According to the related art, 60 dB is achieved, for example, with a traditional design of such radar receivers, or even up to 90 dB with mixers and input modules designed to be especially strong at high powers and driven with correspondingly high currents and local oscillator powers.
An object of the present invention is therefore to provide a device which produces an increase in the dynamic range of frequency-modulated continuous-wave radar.
Another object of the present invention is to provide a receiver for a frequency-modulated continuous-wave radar which can function with a lower power.
Within the scope of the above objects, a goal of the present invention is to provide a receiver for a frequency-modulated continuous-wave radar that is suitable for monolithic integration, such as a microwave monolithic integrated circuit, or MMICxe2x80x94e.g., for applications in an automobile radar system.
Another object of the present invention is to provide a radar receiver with an increased dynamic range and with a low power consumption that is suitable for monolithic integration in particular.
The present invention provides a device for increasing the dynamic range of frequency-modulated continuous-wave radar including a transmitter (13), a send/receive antenna (6), a receiver circuit (9, 10), a circulator (5) for relaying the transmission signals of the transmitter (13) to the send/receive antenna (6) and for diverting the echo signals of a target object to the input of the receiver circuit (9, 10). The receiver circuit (9, 10) is designed to generate on the basis of the transmission signals and echo signals a signal (7) having a differential frequency corresponding to the distance from the target object. An RPC circuit (1) is connected between the input and output of the receiver circuit (9, 10) having a control amplifier device (3). The frequency response of the control amplifier device (3) is selected so that the degree of suppression drops to a predeterminable extent with an increase in the differential frequency above the cut-off frequency (fg) of the control amplifier device (3).
The present invention is explained in greater detail below with reference to the drawings.